-
eory and Applications
lties
J. F ut, A. Young, S. Uemura
C03-76SF0515
USPAS Control Th
Feedback Control of Particle Beam Instabi
ox, J. Cesaratto, T. Mastorides, C. Rivetta, D. Van Winkle, O.
Turg
SLAC
A. Drago, M. Serio
LNF-INFN
J. Flanagan, M. Tobiyama
KEK
D. Teytelman
Dimtel, Inc.
W. Hoefle, R. De Maria
CERN
Work supported by U.S. Department of Energy contract DE-A
-
eory and Applications
Backg
• Fee• Req
Possib
• Exa
• para es
• Kick
Accele
• Mod
• Imp
• Ion
Funda
Intere
Summ
USPAS Control Th
Talk Outline
round - Accelerator Instabilities, Feedback control
dback basicsuirements for beam instability control
le Solutions andTechnical Challenges - State of the Art
Review
mple systems from around the world
llel processing DSP structures, flexible reconfigurable
architectur
er antennas and power structures
rator Diagnosticsvia transient domain techniques
al Growth/damping rates
edances, noise driven motion
and Electron Cloud diagnostics
mental limits to performance and PromisingR&D
Opportunities
sting new directions - ecloud instabilties in the SPS and
LHC
ary
-
eory and Applications
Applic
• Col
• Ligh
Couplperforthe lum
In thebelow
Howe e instability threshold. Forexamp mA instability
threshold.
Feedb
USPAS Control Th
Motivation
ations of charged-particle circular accelerators
liders
t sources
ed-bunch instabilities cause beam loss or reducedmance affecting
the intensity of light sources and
inosity of colliders.
past circular machines were designed to operate the instability
threshold.
ver modern high-current accelerators are routinely run above
thle the Advanced Light Source has 400 mA design current and 40
ack Control provides Stability - AND Accelerator Diagnostics
Active feedback isneeded for design
performance!
-
eory and Applications
The oof a dya desior inp
Regulconsta
Servofollow
Feedb
The e stem performance. There aremany
• RM
• Ste t.
An ad ctuator effort. Peak actuatoreffort
Feedb t parameters or dynamicschang ?
Planty
xternal disturbances
USPAS Control Th
Feedback basics
bjective is to make the outputnamic system (plant) behave inred
way by manipulating inpututs of the plant.
ator problem - keep small ornt
mechanism problem - make a reference signal
ack controller acts to reject the external disturbances.
rror between and the desired value is the measure of feedback
syways to define the numerical performance metric
S or maximum errors in steady-state operation
p response performance such as rise time, settling time,
overshoo
ditional measure of feedback performance is the average or peak
ais almost always important due to the finite actuator range.
ack system robustness- how does the performance change if the
plane? How do the changes in sensors and actuators affect the
system
controller
sensors
actuatorsr u
ey
y
yr
y
-
eory and Applications
Overview
Princi a system
Longit
Transin
Techn
Loop
Pickupo
ProceS
Noiseb
ExamfeN
all ana
sensornoise
z
yv
USPAS Control Th
Coupled-Bunch Feedback Principles - General
ple of Operation-Feedback can be used to change the dynamics
of
udinal - measure - correct E
verse - measure( , ) - kick,
ical issues
Stability? Bandwidth?
, Kicker technologies? Requiredutput power?
ssing filter? DC removal?aturation effects?
? Diagnostics (system andeam)?
ple - the simplest transverseedback idea ( from Galayda,SLS)
log, cable delay for 1 turn
δφ
processnoise
w
u Controller
G
H
BeamδX δY
X' Y '
-
eory and Applications
Equat
Damp ping
USPAS Control Th
Harmonic Oscillators, Revisited
ion of motion where
ing term proportional to - use feedback to ensure negative
dam
ẋ̇ γ ẋ ω02
+ + f t( )= ω0km----=
γ ẋ
0 5 10 15 2010
−1
100
101
Frequency, kHz
Ma
gn
itu
de
0 5 10 15 20−200
−150
−100
−50
0
Frequency, kHz
Ph
ase
, d
eg
ree
s
0 0.2 0.4 0.6 0.8 1 1.2 1.4−6
−4
−2
0
2
4
6x 10
4
Time, ms
Am
plit
ud
e
Impulse response
-
eory and Applications
Bunchstructusamplcoupli
Longitinto a- slopthe focoupli
Trans“kickstransv
For camplitsystem r damping times than shown)
e
n
bunch n+2
Time
USPAS Control Th
Coupled dynamics: multiple bunches
passing through a resonantre excites a wakefield which is
ed by the following bunches - ang mechanism
udinal bunch oscillation translatesphase modulation of the
wakefielde of the wake voltage sampled byllowing bunches determines
theng.
verse Oscillations excite transverse” - magnitude proportional
toerse displacement*current
ertain combinations of wakefieldudes and frequencies the overall
becomes unstable. (In practice the wakefields have much longe
Resonant structur
Vacuum chamber
n+1n+2
bunch n bunch n+1
-
eory and Applications
N cou machines)
Drivin
Broad
Time D
• Pick
• Ban
An all uivalent to a bunch-by-bunch
USPAS Control Th
Normal Modes, Revisited
pled Oscillators,N Normal Modes ( so thousands of modes in
large
g term provides coupling
band ( all-mode) vs. Narrowband Feedback
omain vs. Frequency Domain formalism
up, Kicker signals the same
dwidth Constraints identical
-mode frequency domain system ( with uniform gain) is formally
eq time domain system - identical transfer functions
5-20008545A14
φi-2 φi-1 φi φi+1 φi+2
-
eory and Applications
For an ven-fill eigenmode (EFEM)basis. l modes.
Longig
Real p ndamped natural frequency
The g nt system is unstable.
Two w damping
Lower or Direct RF feedback
Active ative real impedance
USPAS Control Th
Eigenmodes and impedances
even fill pattern the bunch motion can be easily projected into
the e For coupled harmonic oscillators (bunches) there are
norma
tudinal Modal eigenvalues are given by
art of the eigenvalue - exponential growth rate, Imaginary part
- u
rowth rate is proportional to beam current.Above some threshold
curre
ays to fight the instabilities: lower the impedance or use
feedback
ing the impedance is achieved with RF cavity design ( for
HOM’s)
Feedback techniques require signal processing and act as a
neg
N N
Λm dr– iωsαe f rf2E0νs---------------I0Z
effmωrev ωs+( )+ +=
Zeff ω( ) 1ωrf
------- pωrf ω+( )Z pωrf ω+( )p ∞–=
∞
∑=}
Accelerator parameters Beam current Aliasedimpedance
-
eory and Applications
For in
• extr quency,
• amp et damping for a givenimp
• gen t arbitrary if the systemand
Some
• Ban re?)
• DC s phase position, or staticorbi
• Sat
• Noi er)
• Max
• Dia
USPAS Control Th
Processing Requirements
stability control, the processing channel must
act (filter) information at the appropriate synchrotron or
betatron fre
lify it (a net loop gain must be generated, large enough to
cause nedance)
erate an output signal at anappropriate phase(nominally 90
degrees, bu cable delays, pickup and kicker locations are
considered)
technical issues
dwidth/sampling rate ( 500 MHz RF (the bunch separation), or
mo
offset removalfrom the processing channel (e.g. from DC
synchronout offset)
uration on large input errors ( injection, or driven motion)
se in the input channel (e.g. bandwidth reduction via processing
filt
imum supportablegain - limits from noise as well as loop
stability
gnostics (processing system and beam dynamics)
-
eory and Applications
Short
• KEK
• requ cker filling times)
• sets
• Res
•
Many
• KEK
• Nee
Ratio
• Nyq
• Bet
• Syn
• low -bandwidth product)
USPAS Control Th
Technical Challenges
interbunch Interval
-B, ALS, BESSY, PLS, etc. 2 ns, DAFNE 2.7 ns, PEP-II 4.2 ns
ires wideband pickups, kickers ( from required bunch isolation,
ki
required processing bandwidths
olution - Longitudinal damped oscillation rms 0.6 picosecond
- Transverse damped oscillation ~microns
Bunches (many unstable modes)
-B 5120, PEP-II 1746
d to compactly implement bunch by bunch filters
of Frev to Fosc
uist limit Fosc< 1/2 Frev
atron Oscillations grossly undersampled
chrotron oscillations typically oversampled
synchrotron frequency sets scale of required filter memory
(Delay
-
eory and Applications
system
Firstprograinstall
PEP-IPLS,demo
Deteccorrec(optio
Scalaarray,
Samp
May wto redloadrateoscilla
wer
lifier
Kicker oscillator
locked to 9/4×frf
1071 MHz
QPSK modulator
Low-pass filter
structure
To RF stations
Woofer link3.2 1⋅
USPAS Control Th
Block diagram of a longitudinal feedback
Generation DSP,mmable system
ed in:
I, ALS, BESSY-II,DAΦNE and
nstrated at SPEAR
tion at ,tion at 9/4 RFns 11/4, 13/4)
ble processingup to
MAC/sec.
ling at 500 MHz
ant Downsamplinguce computational(match processing
to synchrotrontion frequency)
Low-pass filter
AD
C,dow
nsam
ple
rDSP
Hold
buffer,
DAC
Po
amp
Beam
Phase servo
× ×
BPM
Comb generator
LNA
locked to 6×frf
Master oscillator
2856 MHz
Farm of digitalsignal processors
Kicker
Timing and control6 FRF×
09
-
eory and Applications
USPAS Control Th
HER and LER Systems at PEP-II
-
eory and Applications
Termin
• Tim
• freqSamp utput phase, limits noise,contro
Gener
Gener
wide b
narrow
Maxim
USPAS Control Th
Filter Implementation Options
ology
e domain - bandpass bunch by bunch filters
uency domain - modal selection, notch at Frevling process
suggests discrete time filter (filter generates correct ols
saturation)
al form of IIR filter (infinite impulse response)
al form ofFIR filter (finite impulse response)
andwidth filter - insensitive to variations in machine tune
bandwidth filter - helps reject detector noise
um gain - when noise in front-end saturates DSP processing
yn akyn k– bkxn k–k 0=
M
∑+k 1=
N
∑=
yn bkxn k–k 0=
M
∑=
-
eory and Applications
Each
The ebroadbandw
Exam4 5 6
008;|H|var
= 1.0365; Gain ratio = 1
8 10 12
.1 at 6.595 kHz)
8 10 12
rees at 6.595 kHz)
−
−0.
0.
Coe
ffici
ents
−2
−1
1
2
Mag
nitu
de [d
B.]
−20
−10
10
20
Pha
se [d
eg.]
USPAS Control Th
Example FIR filters
bunch gets an independent controller
xample 6 tap filter (longitudinal, PEP) hasbandwidth - longer
filter would have narroweridth, but comcomitant longer group
delay
ple 5-tap transverse filter for tune 0.190 1 2 3
−15
−10
−5
0
5
10
15
Ratio = 0.57946; ∆Θ = 178.5822; Θvar
= 44.1
0 2 4 6−40
−30
−20
−10
0
10
20
30
40Magnitude of Filter TF (35
0 2 4 6−200
−150
−100
−50
0
50
100
150
200Phase of Filter TF (90.2 deg
deg
Freq. (kHz)
1 1.5 2 2.5 3 3.5 4 4.5 51
5
0
5
1
Taps
Transfer function for a 5 TAP FIR Filter
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50
0
0
0
0
Normalized frequency
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50
0
0
0
0
Normalized frequency
Nominal Tune = 0.19
-
eory and Applications
USPAS Control Th
Baseband transfer Function
-
eory and Applications
USPAS Control Th
RF Transfer Function
-
eory and Applications
ystems
NSLS
• 2 ta
ALS -
• 2 ns
• qua
UVSO
• 16 b
DESY
• 96 n
CESR
• 16 n
Elettra
• 2 ns ctronics
USPAS Control Th
Existing/Example Coupled-Bunch Feedback S
- Galayda, et al (transverse)
p analog FIR (“correlator filter”)
Barry, et al (transverse)
bunch spacing -2 tap analog FIR filter
drature pickups, sum for phase shift
R (Japan) - Kasuga et al. (longitudinal)
unches - 16 analog filters with multiplexing
- Kohaupt et al. (transverse and longitudinal)
s bunch spacing - 70 bunches - 3 tap digital FIR
- Billing, et al (transverse and longitudinal)
s bunch spacing, digital FIR filter
, SLS-Bulfone, et al ( transverse)
bunch spacing, mix of commercial ADC/DSP boards, custom ele
-
eory and Applications
n
From
Quadr it suppression
USPAS Control Th
ALS Transverse Feedback Implementatio
W. Barry
ature processing via 2 pick-ups , Analog 2-tap FIR filter for DC
orb
-
eory and Applications
Exis cont.
PEP-I
• 2 - 4
• gen
• Algo
KEK-B
• 2 ns nts ( no multipliers)
• use ls
SPRIN PGA FIR implementation
iGp - T
• 2nd
• para umbers
• 2 ns
• flex
Libera with FPGA
USPAS Control Th
ting/Example Coupled-Bunch Feedback Systems,
I/ALS/DAFNE/BESSY/PLS - Fox, et al (longitudinal)
ns bunch spacing, 120 - 1746 bunches
eral purpose DSP processing
rithms for FIR and IIR filtering
- Tobiyama, et al (transverse, longitudinal)
spacing, 5120 bunches, 2 tap digital FIR with fixed +1/-1
coefficie
of custom GaAs multiplexing chip set, 16 way muliplexed
channe
G-8(also TLS)Date,et al- 500 MHz,Transverse,4 way multiplexed,
F
etytelman, et al ( general purpose, transverse,
longitudinal)
/3rd Generation technology - reconfigurable gate arrays
llel processor - uneven stepping applicable to various harmonic
n
spacing, 5120 bunches, 16 tap FIR,
ible transverse,longitudinal processor channel
Bunch-by-Bunch ( Instrumentation Technologies) - Multiplexed
A/D
-
eory and Applications
• 3c
• C(DKc
• T
• Lc
• H(5th
• Bind
• Spp
Applic
USPAS Control Th
Example -IGP processing channelrd generation instabilityontrol
technology
ommerical productIMTEL) based on SLAC,
EK, LNF-INFN designollaboration -
ransverse instability control
ongitudinal instabilityontrol
igh-speed beam diagnostics00MHz sampling/roughput rate)
uilds on program instability control and beamiagnostics.
ignificant advance in therocessing speed and densityreviously
achieved.
able to many installations
-
eory and Applications
Inte r technologies
• How lling the speed of light?
• You ery 2 ns., without couplingone
• How iring independentcon
• How ron resolution every 2ns?
These
USPAS Control Th
ractions with the particle beam - pickup and kicke
do you measure thetime of arrivalof a mm long particle beam,
trave
want sub-picosecond rms noise (600 fs), and you need to do it ev
measurement to the other.
do you change the energyof the particle beam bykilovolts, again
requtrol of the bunches every 2 ns?
do you measure thetransverse position of an electron beam with
mic
are interesting transducer and actuator problems!
5-20008545A11
B = 0 B < 1 B 1
1/γ
e – e – e –
-
eory and Applications
Difficumakethe nuBPMburstsdetectfor A/D
Examshowsa resexpon
LongitRF ha
TransDelta-
7288A5
Terminated Lines
67.2400 ns6908A3
USPAS Control Th
Pickup and Frontend technology
lt to process picosecond bunch signals -a periodic coupler
circuit which definesmber of couplers and the center
frequency.impulses are converted to short “tone” for subseqent
delta-sigma or phaseion processing, heterodyning to baseband
input
ple 3 GHz comb, the measured signallittle coupling between the
bunches. ( noteonant bandpass filter would decayentially)
udinal signal - Phase detectagainst 3 Ghzrmonic, baseband phase
error
verse signal- needsAM detection andSigmaprocessing for X and Y
coordinates
8 Cycle Tone Burstto Phase Detector
Impulse from BPM
10–92
57.2400 ns 62.2400 ns4-91
-
eory and Applications
nal processing
ase detection againstsystem. sensitivity
nic
lta/sigma processingdifference signals.
at harmonic of RF, ort baseband
GEN
FROM
D
B
C
A
USPAS Control Th
Frontend sig
Longitudinal - phharmonic of RFscales with harmo
Transverse - Deprovides sum,Amplitude detectprocess directly
a
PHASE
SHIFTER
6xRF
COMB
ERATOR
FAULTBEAM
DETECTOR
PHASE
SERVO
BPMs
AMP
MOTION
To DOWN SAMPLER
MOTION
ERROR MONITOR
A (180◦)
B (0◦) C (Σ)
D (∆)
A (180◦)
B (0◦) C (Σ)
D (∆)
A (180◦)
B (0◦) C (Σ)
D (∆)
A (180◦)
B (0◦) C (Σ)
D (∆)
A
C
B
D
A + C
B + D
D − B
D + C − A − B
B + D − A − C
A + B + C + D
C − A A + D − B − C ∆X
∆Y
Σ
-
eory and Applications
Basic
Like a
• Driv
• (com
• Dow
Longittube
(a trantubespropa
Over-D
a sortbe verbunch
Operaband.
5-20008545A13
vout
vout
USPAS Control Th
“Kicker” Technology Issues
ideas -Transverse Control viaStripline Electrodes
directional coupler
e signal goes “upstream”
bines E-field and B-field kicks)
nstream feed - E and B cancel
udinal kick via periodic drift-
smission line with shielding drift- excitation wave counter-
gates with beam)
amped resonant cavity -
of wideband RF cavity. Q musty low (4 or 5) to kick individuales
nanoseconds apart
ting frequencies in the 1 - 2 GHz
Beam
-
eory and Applications
icks
Longit
Baseb
320 p
QPSKm
Signacn
USPAS Control Th
Six Bunches and associated longitudinal k
udinal output amplifier control signal 2 ns bunch spacing
and risetime
s (2ns/div)
-AModulation
l phase invertsarrier foregative kick
-
eory and Applications
A vi(AdvaLBL)kickerlongituanten
Theallowcorrectransvbeamenerg
USPAS Control Th
ALS Beamline
ew of the ALSnced Light Source,beamline showing Y, X kicker
anddinal kicker
nas.
“kicker” structuresexternal wideband
tion fields toersely deflect thes or to add or subtracty from
the beam.
-
eory and Applications
Trans
Essen aseband ( except for KEK-B, usi
Corne ating beams. Also cleverduty-c
Ampli
Longit
Ceram
Loade SSY ( KEK-B?). Easy tocool. N ted to this design
Drift-tu sed by ALS, PLS, PEP-II.Usefu -II LER, above)
Opera WT power stages ( 200 W)
USPAS Control Th
Kicker Implementations
verse-
tially all striplines. Length limited by bunch spacing.
Operation at bng two sets of kickers/amplifiers)
ll ( CESR) has clever short-circuited design to kick
counter-propagycle modulated kicker driver, as opposed to linear
amplifier drive
fiers - baseband ( 100kHz - 230 MHz)
udinal - Several designs
ic Gap ( UVSOR) - modest shunt impedance
d (damped) Cavity - Designed by LNF-INFN, used by DAFNE, BEeeds
circulator. Reasonable shunt impedance. PEP-II LER upda
be structures - designed by LBL Beam Electrodynamics Group, ul
in-band directivity. Cooling issues for ampere currents ( see
PEP
ting in 1 - 1.5 GHz band. GaAs power amps ( 200 - 500 W), also
T
-
eory and Applications
Many
C
E
O
F
How t
P uency information
O stability threshold. Eachm .
C ted, depends strongly onth
T namics in a single 20 msm sient.
USPAS Control Th
Measuring beam & system dynamics
uses
ontroller algorithm design
stimation of operating margins
ptimization of operating conditions
eedback hardware testing
o characterize an unstable system? Possible approaches
ower Spectrum measurement - no phase information but shows
freq
pen-loop transfer function -measurement is only possible below
inode to be quantified requires a separate network analyzer
sweep
losed-loop transfer function- extracting beam dynamics is
complicae loop configuration.
ransient diagnostics- allow to characterize open and closed-loop
dyeasurement. All unstable modes can be measured in a single
tran
-
eory and Applications
Feedb n extracted bunch
16
USPAS Control Th
Longitudinal Control at the ATF
ack reduces the driven noise spectrum, improves energy spread
i
0 2 4 6 8 10 12 14
10−1
100
101
Frequency (kHz)
Cou
nts
Open loopClosed loop
-
eory and Applications
E t Sources
Thank
USPAS Control Th
ffect of Longitudinal Stability on Synchrotron Ligh
s to Tony Warwick (ALS) for Undulator Spectrum
680 685 690 695 700 705 710 715 7200
1
2
3
4
5
6x 10
−9 Undulator Spectrum − Feedback on (−),off(− −)
Energy ( eV)
No
rma
lise
d O
ptic
al I
nte
nsi
ty (
arb
. u
nits
)
ALS 5th Harmonic Undulator Spectrum 108 mA 84 bunch pattern
-
eory and Applications
Syn
USPAS Control Th
chrotron Light Images
-
eory and Applications
t
stic technique that
the motion of all
l information
Trancharaof an
Lineawhengrow
trigger: or har
Normalfeedback
filter 0
USPAS Control Th
Grow/damp transient measuremen
A transient diagnogenerates
• 1.2MB record ofbunches
• Complete moda
sient measurement tocterize open-loop dynamics unstable
system.
r time control is difficultmaking an exponentially
ing measurement.
softwaredware
Start ofrecording
Filter coefficientset switch
End ofrecording
Adjustablefilter switchbreakpoint
Adjustablehold-offdelay time
filter 1 filter 0 Normalfeedback
-
eory and Applications
PLS
A 30 m
All fillTranssimpliin thismodaeigenvtransie
A singinstabopera
A veryas a fuetc. R
Difficuimpedexciteat a hswam
USPAS Control Th
Grow/damp measurement example from
s long data set with 15 ms open-loop section.
ed bunches participate in the modal motion.formation to the
even-fill eigenmode basisfies the picture - there are three strong
eigenmodes
transient. Fitting complex exponentials to thel motion we
extract estimates of the modalalues for both open and closed-loop
parts of thent.
le measurement like this only characterizes theilities and the
feedback at a single acceleratorting point.
powerful technique- measure modal eigenvaluesnction of beam
current, RF system configuration,
eveals the impedances directly driving the beam
lty - the “free” motion is dominated by the largestance(s). To
study slowly-growing modes, you canthe mode of interest before the
study - it then startsigher ( detectable) amplitude. In a while it
is
ped by the fast modes.
-
eory and Applications
ent
ased measurement of in-
grow-damp transients,cies, as the watere is varied ( this
sweepsmpling frequency of the−400
−20
0
20
40
60
80
100
ℜ(Z
|| ) (
kΩ)
−400−60
−40
−20
0
20
40
60
ℑ(Z
|| ) (
kΩ)
USPAS Control Th
ALS HOM Complex Impedance Measurem
These techniques allow beam-bsitu HOM impedances
The measurement is made viameasuring complex frequentemperature
of the cavity structurthe HOM frequency across the sabeam)
−300 −200 −100 0 100 200 300 400Frequency offset from resonance
(kHz)
Fr=2.8532 GHz, R
s = 97±3kΩ; Q = 24000±2000; R
s/Q =4±0.3 Ω
−300 −200 −100 0 100 200 300 400Frequency offset from resonance
(kHz)
-
eory and Applications
DAFN
• i
• qinind
Flexibnovel
• sth
• twd
• qsin
80 100 120
DualNotch
80 100 120
USPAS Control Th
Quadrupole instability control
E e+/e-collider at LNF
ncreased operating currents
uadrupole mode longitudinalstabilities have appeared (thestalled
system suppresses theipole modes).
le DSP code implemented aquadrupole control filter
oftware programmability ofe DSP farm
o parallel control paths foripole and quadrupole modes.
uadrupole control has beenuccessful, allowing a 20%crease in
luminosity.
0 20 40 60
−40
−20
0
20
40
Frequency (kHz)
Gai
n (d
B)
0 20 40 60−200
−100
0
100
200
Frequency (kHz)
Pha
se (
deg)
-
eory and Applications
lysis
Advan
Comp aches allow measurementsof gro
In a tra mode-by-mode narrowbandmeasu
From rowth rates, but alsooscilla
Large
Difficu
Expon
Large
USPAS Control Th
Advantages and difficulties of transient ana
tages
lementary to narrowband frequency domain detection. Both
approwth/damping rates.
nsient all unstable modes are measured at once - much faster
thanrement when there are hundreds of unstable modes
a transient measurement we get complex eigenvalues - not only
gtion frequencies.
datasets - information about the motion of every bunch
lties
ential growth rates - easy to lose control of the beam.
datasets
-
eory and Applications
Ultim
What ance)?
Sever
I). Noi several stages -
Front namic range, steady-stateoffsets ceivers typically 10 - 20
dBabove A/D noise or DSP
Proce oise (broadband) is onesystem ater in contribution.Narrow
lp with reduced sensitivityto ma t
Power expensive way to increasegain (m
Outpu scillation amplitude fromwhich mplicated
Driven mit on achievable gain
Intere 802,2010
USPAS Control Th
ate/Practical Limits to Instability Control
Limits theMaximum Gain(e.g. fastest growth rate, or allowed
imped
al Mechanisms
se in feedback filter bandwidth, limits on noise saturation.
Gain is from
End (BPM to baseband signal) gain limited by required
oscillation dy(synchronous phase transients, orbit offsets). Noise
floors in the re
A/D quantizing noise.Damped equilibrium noise floor is not set
by
ssing Block - gain limited by noise in filter bandwidth.
Quantizing n limit - noise from RF system or front-end circuitry is
typically greband filters help with broadband noise. Broad filter
bandwidths he
chine tunes, operating point - or variations of dynamics with
curren
stages - gain scales with kicker impedance, sqrt(output power).
Anore kickers, more output power).
t power (actually maximum kicker voltage) determines maximum o
linear (non-saturated) control is possible. Saturated behavior is
co
noise ( e.g. from RF system, or from other excitations) may set
li
sting Movie - loss of Control in PEP-II from RF noise PRST
13:052
-
eory and Applications
art II
II) Sta s. control frequency)
Relate
For cir n pickup)
limit s ver control band
Appro
L
R
U
Negat for causal systems you paythe pr
USPAS Control Th
Ultimate/Practical Limits to Instability Control, p
bility of the feedback loop itself, (e.g. limits on phase shift
and gain v
d to time delay between pickup, processing, and actuator
cular machines (systems with kick signal applied on later turn
tha
et by revolution time, fastest growth rates, and filter phase
slope o
priate for optimal control theory applications
QR
obust Control
ncertain Systems
ive group delay over a portion of the frequency band is
possible, butice in increased phase slope away from the negative
region
-
eory and Applications
1 - 4 G
Gener le FPGA architectures.Softwa AC/KEK/CERNcollab filters.
Allows I&Qproce
Low G
• pote dback in ILC
• Very ks, using electronic orelec
Kicker
existin with heating at high beamcurren
RF Fe xisting analog and hybridanalog and also LHC) are
nearingtechno ital RF processing channellook v
USPAS Control Th
Promising Areas for R&D Efforts
S/sec. processing channels
al-purpose reconfigurable building blocks - based on
reconfigurabre configured for multiple longitudinal/transverse
applications. SL
oration has prototypes in evaluation, development of novel
controlssing streams (2X sampling)
roup Delay processing channels
ntial applications in Energy Recovery Linacs, IP collision point
fee
low group delay (e.g. 10s of nanosecond scale) FIR/IIR filter
bloctro-optic technologies
structures
g drift tube, stripline and damped cavity kickers all have
issuests, residual HOM content
edback techniquesto reduce impedances seen by the Beam - the
e/digital RF feedback techniques in the LLRF systems at PEP-II
(logy and operational limits. Efforts to develop a low group delay
dig
ery attractive
-
eory and Applications
rts
Ongoi
Proton PS injector)
• Pho
• Cou
• Sing
Resea
• Sim
• Mac ulations
• Wh
• Dev
Kicker
• Res icker
• Use ? overdamped cavity?
USPAS Control Th
LHC/SPS Ecloud driven instability R&D Effo
ng project SLAC/LBL/CERN via US LARP
machines,Ecloud driven instability - impacts upgraded LHC ( and
S
toelectrons from synchrotron radiation - attacted to positive
beam
pled-dynamics, electrons act as lens to kick transversely
le-bunch effect - head-tail (two-stream) instability
rch directions
ulations
hine measurements - understand required bandwidth, validate
sim
at sort of feedback control is feasible?
elopment of 4 GS/sec. processing channel demonstrator
structures
earch effort to investigate useful 1 - 2 Ghz bandwdith
transverse k
periodic slotline ( stochastic cooling)? Array of 1/4 wave
striplines
-
eory and Applications
Eclou2010.injectiTimetransv(Junebetwe
TMCIbunchinstab
data tpickupsampl
We nsimulabeam
Studie
pickupquant
bunch 47
50 100slice
bunch 119
50 100slice
USPAS Control Th
SPS MD Studies
d studies June 2009, April 2010 JulyVertical Instability
develops after
on of second batch, within 100 turns.domain shows bunch charge,
anderse displacement 1E11 p/bunch2009). Roughly 25 slices (250
ps)en displacement maxima and minima
Studies July/August 2010. Singleinjection at 1.3E11 (3E11).
Vertical
ility develops - time scales of 1000 turns
aken via exponentially-tapered striplines, delta/sigma
processing at baseband.ed 20 or 40 GS/sec.
eed MD data to compare beamtions and dynamics models, -
extractdynamics necessary to design feedback.
s of bandwidth of motion, tune shifts
s -Noise, transverse resolution well-ified
0 50 100−400
−300
−200
−100
0
100
200
300
400
500 Vertical displacement of
slice
SU
M /
DIF
F s
igna
ls (
a.u)
0−1
−0.8
−0.6
−0.4
−0.2
0
0.2
0.4
0.6
0.8
1
Ver
tical
dis
plac
emen
t (a.
u)
SUMDIFF
0 50 100−400
−300
−200
−100
0
100
200
300
400
500 Vertical displacement of
slice
SU
M /
DIF
F s
igna
ls (
a.u)
0−1
−0.8
−0.6
−0.4
−0.2
0
0.2
0.4
0.6
0.8
1
Ver
tical
dis
plac
emen
t (a.
u)
SUMDIFF
-
eory and Applications
MD da 2 RF voltages
Pre-pr ongitudinal motion
9 and
ug_09/)
1E11 a)
Injecti e)
Movie able)
Movie 19 e-clouds)
Movie signal by slice
Movie
Movie troid
These he system
We ne edback control
USPAS Control Th
Movies of June 16, 2009 SPS MD
ta at 1E11 P/bunch, with three chromaticity values (.1,.2 and
-.1),
ocessing includes equalization (cable response), suppression of
l
(www.slac.stanford.edu/~rivetta/e-clouds/movies_Aug0
also inhttp://www.slac.stanford.edu/~dandvan/e-clouds/a
P/bunch, 25 ns separation, 72 bunches/batch ( June 2009 MD
dat
on of batch 1 ( stable) followed by 2nd batch ( which goes
unstabl
1-Vdspl_bunch_47.avi Vdisplacement for bunch 47 1st batch
(st
2 -Vdspl_bunch_119.avi Vdisplacement for bunch 47 2nd batch
(#1
3 - tune_s.avi Sliding Window spectrogram of Bunch 117
vertical
4 -centroid.avi Centroid tune shift along 620 turns
5 -rms.avi RMS of slice motion with respect to the bunch cen
animations help show the complexity and non-linear behavior of
t
ed to extract simpler model dynamics to use to design/estimate
fe
-
eory and Applications
Feed of ecloud/beam
Goal - lisms
• Equ
• Mod
• grow
• tune cess)
sliding
• slice
• vs.
RMS t e evolution, charge loss)
Estim s/noise in receivers, powerstages
Recen dels to data
Critica ne shifts, internal modes
USPAS Control Th
back Estimation- requires quantitative knowledgedynamics
develop quantitative analysis methods, normal-mode, other
forma
alization, suppression of longitudinal motion effects
es within the bunch (e.g. bandwidth of feedback required)
th rates of modes (e.g. gain of feedback channel)
shifts, nonlinear effects (e.g. Stability, robustness of
feedback pro
windowFFT techniques - check tunes, tune shifts
FFTs (tune per slice)
time (modes within a bunch)
echniques- on SUM and Delta (estimation of motion of the beam,
tim
ate impacts - injection transients, external excitations,
imperfection.
t Emphasis - System Identification methods to fit
coupled-oscillator mo
l to estimate - required sampling rate (bandwidth), growth
rates, tu
-
eory and Applications
cale?
Frequ
sampl table modes)
Scale
• mea
SPS -
• 16 s evolution frequency
• 16 t
KEKB
• 1 sa on frequency.
Thesc ntroller model isnot verydiffere
What kicker structures, plusthe ne ates may be comparable
Impor eam. Controller complexity
USPAS Control Th
E-cloud Feedback Channel - Complexity? S
ency spectrograms suggest:
ing rate of 2 - 4 GS/sec. (Nyquist limited sampling of the most
uns
of the numeric complexity in the DSP processing filter
sured in Multiply/Accumulate operations (MACs)/sec.
5 GigaMacs/sec. (6*72*16*16*43kHz)
amples/bunch per turn, 72 bunches/stack, 6 stacks/turn, 43 kHz
r
ap filter (each slice)
(existing iGp system) -8 GigaMacs/sec.
mple/bunch per turn, 5120 bunches, 16 tap filters, 99 kHz
revoluti
aleof an FIR based control filter using the single-slice
diagonal cont than that achieved to date with the coupled-bunch
systems.
isdifferent is therequired sampling rateandbandwidthsof the
pickup,ed to havevery high instantaneous data rates, though the
average data r
tant dynamics difference - Ecloud tune shifts, even for
stabilized b
-
eory and Applications
Develexpon
Can b
Estimchaoti
Idea -seque
Time dfunctio
Frequ
Can b
Valuabcontro
Progre
400W
Tunne /sec. D/A
USPAS Control Th
Driven Beam Experiments
op excitation technique using existingential striplines
e frequency domain or time domain study
ate dynamics below instability threshold (pre-c motion, see tune
shifts below threshold)
use 4 GS/sec. DAC hardware todrive noisences onto selected
bunch(es)
omain sequences - transform, average (transfern estimator)
ency response of internal structure and modes
e done as excitation in simulation, too.
le step in development of any possible feedbackller (Back
End)
ss - Synchronized excitation code
(4 100W) 20 - 1000 MHZ amplifiers ordered
l “cart” in progress for 2011 SPS MD Doublet Response 4 GS
-
eory and Applications
DAFN Diamond et al. all havesignifi ll routinely operate
wellabove l and custom hardware.
Thein o the driving impedances.Runni rstand the practical limits
ofthese argin limit for control of lowmode issioned.
The te performance of thesesystem n gain and phase fromloop s
nore. Recent commercialactivit ck systems more feasible.Signifi
beams.
The d re very useful in validatingdynam hey also provide many
veryunique edances). Theflexibilityof the eds as the accelerators
weremodifi novel IIR control filters, orthe qu
The n ew ideas in control
USPAS Control Th
The State of the Art
E, KEK-B, CESR, PEP-II, ALS, BESSY-II, PLS, Elettra, ESRF,cant
experience running multi-bunch instability control systems. A
instability thresholds. Other facilities developing mix of
commercia
stabilitiesthemselves are proportional to current, and
proportional tng these facilities at higher currents requires some
analysis to undeinstability control systems. PEP-II pushed the
fundamental phase ms, and a special low group delay channel ( the
“woofer”) was comm
chnology of these systems may evolve, but thefundamental
limitsto thes, e.g. thesaturation effects from noiselimiting the
gain, and the limits o
tabilityof the feedback loop, are the central limits we must
never igy in high speed FPGA platforms make 1-4 GS wideband
feedbacant challenges exist in the transducers which sense and
control
iagnostics possible with the programmable DSP based systems aics
and understanding the performance of the instability control.
Taccelerator diagnostics(such as measurement of complex HOM imp
se systems has been an opportunity to address several control
need (such as the addition of harmonic cavities to the ALS,
requiringadrupole mode control at DAFNE)
ew directions in Ecloud control for the SPS and LHC may require
n
-
eory and Applications
Multi-b
Proble eratemodulation offilling
• Des
• diffe des) and narrowband HOMstru
• Tec
• Issu
• Sen
Likely
Gener 8 Gs/sec. sampling rates.Softwa loud control.
Wideb
Very lo using electronic or electro-optic t
USPAS Control Th
Summary
unch instability control-
m can be addressed withimpedance control, carefulcavity tuning,
delibpatterns, and/or active feedback
ign choices - all-mode vs. selected modes
rence between damped HOM structures (e.g. bands of unstable
moctures
hnology choices - processing approaches
es of injected noise, required output power
sitivity to variations in operating configurations
Areas for future work
al-purpose reconfigurable building blocks - based on 1 GS/sec.
tore configured for multiple longitudinal/transverse applications,
Ec
and kicker and pickup technologies ( GHz bandwith systems)
w group delay (e.g. 10s of nanosecond scale) FIR/IIR filter
blocks,echnologies
-
eory and Applications
Pickup
( histo
Cable
Hybrid
• Cab
• Issu Bessel Filters
Data A , 10 or 40 PS/sample)
Offline
Equal udinal motion
RMS
• on S volution, charge loss)
FFT b
• slice
• with
USPAS Control Th
SPS Instrumentation - setup
s- wideband ( exponential taper) striplines ( T. Linnecar)
ry of directivity, past use in P-Pbar program)
plant from SPS Tunnel to Faraday cage ( instrument room)
receiver ( Anzac H9 Hybrids )
le delays trimmed, matched, hybrids selected for matching
es with 1700 MHz propagating modes - use of800 MHz ( 1 GHz
etc.)
cquisition ( vertical plane) in Tektronix fast scope (2.5 GHz
bandwidth
data analysis in Matlab ( and Python)
isation of stripline signal ( thanks WH and RDM), removal of
longit
techniques ( with subtraction of DC transient)
UM and Delta ( estimation of motion of the beam, head-tail time
e
ased sliding window techniques
by slice ( tune shifts within a bunch)
in bunch ( bandwidth or internal modes)
-
eory and Applications
Const
• Con hift)
• DC
• Fre
FIR Fi
Desig
• Letwav
• Pha
• Set(DC
• Rescha
What avities).
What
10 20 30 40Frequency (kHz)
USPAS Control Th
A possible controller design approach
raints
trol of phase & gain at the oscillation frequency Fs (90
degree phase s
rejection
quency selectivity
lter implementation:
n approach
filter impulse response sample a sinee at the oscillation
frequency.
se and gain adjustments are simple
sum of the impulse response to 0 rejection)
ulting filter has bandpassracteristic around the Fs
if the oscillation frequency changes with current?(ALS, Harmonic
C
if quadrupole as well as dipole oscillations are present?
(DAFNE)
yn bkxn k–k 0=
M
∑=
0 10 20 30 40−30
−20
−10
0
10
20
30
Frequency (kHz)
Gai
n (d
B)
0−300
−200
−100
0
100
200
Pha
se (
degr
ees)
Feedback Control of Particle Beam InstabiltiesTalk
OutlineMotivationFeedback basicsCoupled-Bunch Feedback Principles -
General OverviewHarmonic Oscillators, RevisitedCoupled dynamics:
multiple bunchesNormal Modes, RevisitedEigenmodes and
impedancesProcessing RequirementsTechnical ChallengesBlock diagram
of a longitudinal feedback systemHER and LER Systems at
PEP-IIFilter Implementation OptionsExample FIR filtersBaseband
transfer FunctionRF Transfer FunctionExisting/Example Coupled-Bunch
Feedback SystemsALS Transverse Feedback ImplementationExample -IGP
processing channelInteractions with the particle beam - pickup and
kicker technologiesPickup and Frontend technologyFrontend signal
processing“Kicker” Technology IssuesSix Bunches and associated
longitudinal kicksALS BeamlineKicker ImplementationsMeasuring beam
& system dynamicsLongitudinal Control at the ATF
Effect of Longitudinal Stability on Synchrotron Light
SourcesSynchrotron Light ImagesGrow/damp transient
measurementGrow/damp measurement example from PLSALS HOM Complex
Impedance MeasurementQuadrupole instability controlAdvantages and
difficulties of transient analysis
Ultimate/Practical Limits to Instability Control, part
IIPromising Areas for R&D EffortsLHC/SPS Ecloud driven
instability R&D Efforts
SPS MD StudiesMovies of June 16, 2009 SPS MDFeedback Estimation-
requires quantitative knowledge of ecloud/beam dynamicsE-cloud
Feedback Channel - Complexity? Scale?Driven Beam ExperimentsThe
State of the ArtSummarySPS Instrumentation - setupA possible
controller design approach